1. Field of the Invention
The present invention relates to a projection image display apparatus using an image display element.
2. Related Background Art
A reflection image display element such as a reflection LCD panel reflects incident illumination light and forms image light by performing modulation in accordance with an image signal. For example, Japanese Patent Application Laid-Open No. 2000-284228 discloses a projection image display apparatus which performs color separation/synthesis and projecting an image by using such a reflection image display element, a color selective retardation plate for rot 90xc2x0 the polarization direction of only light in a given wavelength region, and a polarizing beam splitter having a polarization split surface having the properties of reflecting S-polarized light and transmitting P-polarized light.
FIG. 15 shows an arrangement of a conventional projection image display apparatus. This apparatus includes a light source 101, polarizing plate 102, color selective retardation plates 103, 104, and 105, polarizing beam splitters 106, 107, 108 and 109, reflection liquid crystal display elements 110R, 111B, and 112G, and projection lens 113.
The unpolarized light emitted from the light source 101 is converted into linearly polarized light (P-polarized light) by the polarizing plate 102, and the polarization direction of only red (R) light is rotated by 90xc2x0 by the color selective retardation plate 103 to convert the red light into S-polarized light. The red light which is S-polarized light is incident on the polarizing beam splitter 106 and reflected, and green (G) light and blue (B) light, other than the red light, which are P-polarized light, are transmitted through the polarizing beam splitter 106. With this operation, the unpolarized light is color-separated into red light, and green light and blue light.
The red light is reflected by the polarizing beam splitter 108 and incident on the reflection liquid crystal display element 110R. The green light and blue light are incident on the polarizing beam splitter 104, by which the polarization direction of only the blue light is rotated by 90xc2x0 to convert the light into S-polarized light.
The polarizing beam splitter 107 reflects the blue light which is S-polarized light and transmits the green light which is P-polarized light, thereby color-separating these light components. The blue light and green light are then incident on the reflection liquid crystal display elements 111B and 112G, respectively.
Of the red light modulated by the reflection liquid crystal display element 110R, the S-polarized light component is reflected by the polarizing beam splitter 108 and returns to the light source 101 side, and the P-polarized light component is transmitted through the polarizing beam splitter 108 to become projection light.
Of the light modulated by the reflection liquid crystal display element 111B, the S-polarized light component is reflected by the polarizing beam splitter 107 and returns to the light source 101 side, and the P-polarized light component is transmitted through the polarizing beam splitter 107 to become projection light.
Of the light modulated by the reflection liquid crystal display element 112G, the P-polarized light is transmitted through the polarizing beam splitter 107 and returns to the light source 101 side, and the S-polarized light is reflected by the polarizing beam splitter 107 to become projection light.
The blue light and green light both comprising projection light are incident on the color selective retardation plate 105, by which the polarization direction of the blue light is rotated by 90xc2x0, thereby uniformly converting both the blue light and the green light into S-polarized light.
The blue light and green light which have become S-polarized light are reflected by the polarizing beam splitter 109, whereas the red light which is P-polarized light is transmitted through the polarizing beam splitter 109. With this operation, the red light, green light, and blue light are synthesized into one light. This light is then projected through the projection lens 113 to display a color image.
In general, a polarizing beam splitter (i.e., a polarization split surface) exhibits ideal polarization split performance as shown in FIG. 16 with respect to light incident on this polarization split surface at 45xc2x0, but exhibits imperfect characteristics as shown in FIG. 17 with respect to light incident at angles deviating from 45xc2x0.
This is because since an optical thin film forming a polarization split surface acts on optical performance at nxc2x7dcosxcex8 where n is the refractive index of the thin film, d is the thickness of the thin film, and xcex8 is the incident angle of light, the optical performance changes in accordance with a change in the incident angle xcex8.
As shown in FIG. 2, as an illumination system for a projection image display apparatus, an illumination system designed to uniformly illuminate the reflection image display element is widely used.
The light emitted from a light source 1 is incident on a point on a reflection liquid crystal display element R with a divergent angle 2xcfx89 through a condenser lens system 5 and field lens system 7. For this reason, light is incident on the polarization split surface in the range from (45xe2x88x92xcfx89)xc2x0 to (45+xcfx89)xc2x0. Therefore, light incident on the polarization split surface at an angle deviating from 45xc2x0 is not perfectly separated into a P-polarized light component and S-polarized light component.
In this case, since the polarization direction of light reflected by a reflection liquid crystal display element ready to display black is the same as that of light incident on the reflection image display element, the light reflected by the reflection image display element must be returned to the light source side through the polarizing beam splitter and detected by the polarizing beam splitter.
However, since the light reflected by the reflection image display element ready to display black is incident on the polarizing beam splitter with a spread corresponding to the incident angle 2xcfx89, light incident at an angle deviating from 45xc2x0 is not detected by the polarizing beam splitter and becomes so-called leakage light, which is projected through the projection lens. As the amount of leakage light increases, displayed black appears as if it was floating, and the contrast of an image may decrease.
For preventing above situation, one aspect of the present invention is to provide a projection image display apparatus comprising an illumination optical system which illuminates an image display element with light from a light source and a projection optical system which projects light from the image display element through two,polarization split surfaces, wherein when an occurrence ratio of leakage light on one polarization split surface with respect to a light ray having a wavelength xcex is represented by analysis performance K(xcex), relative visibility of the human eye is represented by Y(xcex), and a wavelength region of light rays incident on the one polarization split surface is represented by a range of xcex1 to xcex2, a value M given by   M  =            ∫              λ        1                    λ        2              ⁢                  Y        ⁢                  (          λ          )                    ⁢              K        ⁢                  (          λ          )                    ⁢              xe2x80x83            ⁢                        ⅆ          λ                /                              ∫                          λ              1                                      λ              2                                ⁢                                    Y              ⁢                              (                λ                )                                      ⁢                          xe2x80x83                        ⁢                          ⅆ              λ                                          
is set as a leakage light amount on the polarization split surface, of the light rays incident on one of the two polarization split surfaces which is located on the image display element side whose angles with respect to an optical axis correspond to 55% of a maximum angle of the incident light rays with respect to the optical axis, light lays of which incident angle with respect to said image display element is larger is set as first light ray and light rays of which incident angle with respect to said image display element is smaller is set as second light ray, respectively, and
L less than 0.006xe2x80x83xe2x80x83(1)
is satisfied when a light shielding characteristic value L on the two polarization split surfaces is represented by
L=[(M1)axc2x7(M1)b+(M2)axc2x7(M2)b]/2
where (M1)a is the amount of leakage light of the first light ray on the polarization split surface on the image display element side, (M2)a is the amount of leakage light of the second light ray on the polarization split surface on the image display element side, (M1)b is the amount of leakage light of the first light ray on the polarization split surface on the projection optical system side, and (M2)b is the amount of leakage light of the second light ray on the polarization split surface on the projection optical system side.
In this case, as relative visibility of the human eye, for example, a value defined by international standards may be used.
In addition, leakage light is light, of a first polarized light component, which is transmitted through a polarization split surface that reflects light having a first polarized light component and transmits light having a second polarized light component perpendicular to the first polarized light component, or light, of the second polarized light component, which is reflected by the polarization split surface. Furthermore, leakage light is light, of the first polarized light component, which is reflected by a polarization split surface that transmits light having the first polarized light component and reflects light having the second polarized light component perpendicular to the first polarized light component or light, of the second polarized light component, which is transmitted through the polarization split surface.
The above xe2x80x9clight ray, of the light rays incident on the polarization split surface, whose angles with respect to the optical axis correspond to 55% of the maximum angle of the incident light rays with respect to the optical axisxe2x80x9d and xe2x80x9cfirst and second light raysxe2x80x9d will be described with reference to FIG. 18.
Referring to FIG. 18, an optical system has an optical axis Lo, and a polarization split surface F is formed on a polarizing beam splitter G on the image display element side.
A total light beam (solid lines) incident on the polarization split surface F has a divergent angle xcex2 with respect to the optical axis Lo (2xcex2 centered on the optical axis). In addition, a light beam (dotted lines) having a divergent angle xcex2xe2x80x2 (2xcex2xe2x80x2 centered on the optical axis) corresponding to 55% of the angle xcex2 with respect to the optical axis Lo produces an illumination light amount about xc2xd that by the total incident light beam on the polarization split surface F.
In the present invention, therefore, of light rays L1 and L2 having the angle xcex2xe2x80x2 with respect to the optical axis Lo, the light ray L1 which is incident on the polarization split surface at a larger angle (xcex1+) is defined as the xe2x80x9cfirst light rayxe2x80x9d (so-called an upper light ray on an optical cross-section), and the light ray L2 incident at a smaller angle (xcex1xe2x88x92) is defined as the xe2x80x9csecond light rayxe2x80x9d (so-called a lower light ray).
In the above apparatus, the light shielding characteristic value L preferably satisfies
L less than 0.002xe2x80x83xe2x80x83(2).
In the above apparatus, the image display element is preferably a reflection image display element.
The above apparatus preferably comprises: first, second, and third reflection image display elements; a light beam splitting system which splits light from the light source into a plurality of light beams and substantially uniforms intensities of the light beams; a color separation system which separates light from the light beam splitting system into a first wavelength region light and second and third wavelength region lights; a first polarization split surface which guides the first wavelength region light from the color separation system to said first reflection image display element and analyzes light from the first reflection image display element; a first color selective retardation plate which changes a polarization direction of only the second wavelength region light of the second and third wavelength region light from the color separation system; a second polarization split surface which splits the second and third wavelength region light from the first color selective retardation plate, which have polarization directions perpendicular to each other to guide the lights to the second and third reflection image display elements, respectively, synthesizes lights from the second and third reflection image display elements, and analyzes lights from the second and third reflection image display elements; a second color selective retardation plate which changes a polarization direction of only one of the second and third wavelength region lights from the second polarization split surface; and a third polarization split surface which synthesizes the second and third wavelength region lights from the second color selective retardation plate and the first wavelength region light from the first polarization split surface, guides the light components to the projection optical system, and analyzes light components from the first, second, and third reflection image display elements.
In the above apparatus, the apparatus comprises first, second, and third reflection image display elements, and the illumination optical system splits light from the light source into first, second, and third wavelength region lights, and guides the lights to the first, second, and third reflection image display elements, respectively.
In the above apparatus, light reflected by one of said first, second, and third reflection image display elements is reflected by the polarization split surface located on the reflection image display element side, is transmitted through the polarization split surface located on the projection optical system side, and reaches the projection optical system, analysis performance Ka(xcex) of the polarization split surface on the reflection image display element side is represented by
Ka(xcex)=1xe2x88x92Tpa(xcex)
where Tpa(xcex) is a transmittance of P-polarized light through the polarization split surface on the reflection image display element side, analysis performance Kb(xcex) of the polarization split surface on the projection optical system side is represented by
Kb(xcex)=Tsb(xcex)
where Tsb(xcex) is a transmittance of S-polarized light through the polarization split surface on the projection optical system side, and analysis performance K(xcex) of the two polarization split surfaces is represented by                               K          ⁡                      (            λ            )                          =                              Ka            ⁡                          (              λ              )                                ·                      Kb            ⁡                          (              λ              )                                                              =                              (                          1              -                              Tpa                ⁡                                  (                  λ                  )                                                      )                    ·                                    Tsb              ⁡                              (                λ                )                                      .                              
In the above apparatus, light transmitted through the polarization split surface on one of the first, second, and third reflection image display element sides is reflected by the polarization split surface on the projection optical system side and reaches the projection optical system, analysis performance Ka(xcex) of the polarization split surface is represented by
Ka(xcex)=Tsa(xcex)
where Tsa(xcex) is a transmittance of S-polarized light through the polarization split surface on the reflection image display element side, analysis performance Kb(xcex) of the polarization split surface is represented by
xe2x80x83Kb(xcex)=1xe2x88x92Tpb(xcex)
where Tpb(xcex) is a transmittance of P-polarized light through the polarization split surface on the projection optical system side, and analysis performance K(xcex) of the two polarization split surfaces is represented by                               K          ⁡                      (            λ            )                          =                              Ka            ⁡                          (              λ              )                                ·                      Kb            ⁡                          (              λ              )                                                              =                              Tsa            ⁡                          (              λ              )                                ·                                    (                              1                -                                  Tpb                  ⁡                                      (                    λ                    )                                                              )                        .                              
In the above apparatus, light transmitted through the polarization split surface on one of the first, second, and third reflection image display element sides is transmitted through the polarization split surface on the projection optical system side and reaches the projection optical system, analysis performance Ka(xcex) of the polarization split surface is represented by
Ka(xcex)=Tsa(xcex)
where Tsa(xcex) is a transmittance of S-polarized light through the polarization split surface on the reflection image display element side, analysis performance Kb(xcex) of the polarization split surface is represented by
Kb(xcex)=Tsb(xcex)
where Tsb(xcex) is a transmittance of S-polarized light through the polarization split surface on the projection optical system side, and analysis performance K(xcex) of the two polarization split surfaces is represented by                               K          ⁡                      (            λ            )                          =                              Ka            ⁡                          (              λ              )                                ·                      Kb            ⁡                          (              λ              )                                                              =                              Tsa            ⁡                          (              λ              )                                ·                                    Tsb              ⁡                              (                λ                )                                      .                              
In the above apparatus, light reflected by the polarization split surface on one of the first, second, and third reflection image display element sides is reflected by the polarization split surface on the projection optical system side and reaches the projection optical system, analysis performance Ka(xcex) of the polarization split surface is represented by
Ka(xcex)=1xe2x88x92Tpa(xcex)
where Tpa(xcex) is a transmittance of P-polarized light through the polarization split surface on the reflection image display element side, analysis performance Kb(xcex) of the polarization split surface is represented by
K2(xcex)=1xe2x88x92Tpb(xcex)
where Tpb(xcex) is a transmittance of P-polarized light through the polarization split surface on the projection optical system side, and analysis performance K(xcex) of the two polarization split surfaces is represented by                               K          ⁡                      (            λ            )                          =                              Ka            ⁡                          (              λ              )                                ·                      Kb            ⁡                          (              λ              )                                                              =                              (                          1              -                              Tpa                ⁡                                  (                  λ                  )                                                      )                    ·                                    (                              1                -                                  Tpb                  ⁡                                      (                    λ                    )                                                              )                        .                              
In calculating leakage light amounts, if wavelength regions subjected to integration are defined such that the blue wavelength region is defined by 430 to 490 nm; the green wavelength region, 500 to 580 nm; and the red wavelength region, 590 to 650 nm, contrast values on the R, G, and B optical paths can be properly estimated.
In the above apparatus, the image display element is preferably a reflection liquid crystal display element.
The above apparatus preferably comprises three polarizing beam splitters and one dichroic prism.
The above apparatus preferably comprises three polarizing beam splitters and one dichroic mirror.
In the above apparatus, each of the first, second, and third wavelength region light components preferably corresponds to one of red, green, and blue light components.